The effect of cyclic AMP and dibutyryl cAMP on DNA synthesis of chick embryo fibroblasts in culture will be further studied. In particular, cells infected with avian myeloblastosis virus have been shown to incur an early increase in DNA synthesis relative to uninfected cells. It is planned to study the effect of added cyclic AMP and dibutyryl cyclic AMP on cell infected with either the Rous sarcoma virus or the avian myeloblastosis virus.